Offloading XDG cache home to tmpfs

#Usage.md

1. Configure /tmp as per fstab, adjust size if needed
2. Copy xdg-cache.service to /etc/systemd/user/xdg-cache.service
3. Copy xdg-cache.sh to /usr/local/bin/xdg-cache.sh and then chmod +x /usr/local/bin/xdg-cache.sh
4. Run systemctl --user enable xdg-cache.service as the user that needs this service

fstab

tmpfs						/tmp		tmpfs	defaults,noatime,nosuid,nodev,mode=1777,size=24G	0 0

xdg-cache.service

[Unit]
Description=Synchronises XDG cache between disk and tmpfs for %u
Before=default.target

[Service]
Type=oneshot
RemainAfterExit=true
ExecStart=/usr/local/bin/xdg-cache.sh ram
ExecStop=/usr/local/bin/xdg-cache.sh
StandardOutput=journal
StandardError=journal
TimeoutStopSec=1m

[Install]
WantedBy=default.target

xdg-cache.sh

#!/usr/bin/env bash

PERSIST_DIR="$HOME/.cache"
TMP_DIR="/tmp/$USER/.cache"

if [[ "$1" == "ram" ]]; then
    # to ram
    if [ -d "$PERSIST_DIR" ]; then
        #TIME='%C  %Us user %Ss system %es total' time rsync -aq "$PERSIST_DIR/" "$TMP_DIR"
        mkdir -p "$TMP_DIR" "$TMP_DIR-upper"
        TIME='%C  %Us user %Ss system %es total' time unionfs \
		-o rw,async,exec,suid,dev,nonempty,default_permissions,allow_other \
		-o use_ino,cow,statfs_omit_ro,hide_meta_files,max_files=65536 \
		"$TMP_DIR-upper=RW:$PERSIST_DIR=RO" "$TMP_DIR"
    fi
elif [ -d "$TMP_DIR" ]; then
    # to disk
    TIME='%C  %Us user %Ss system %es total' time rsync -ai --delete --delete-excluded --ignore-missing-args \
        --exclude='/google-chrome' \
        --exclude='/yay/*/' \
        --exclude='/pip' \
        --exclude='/kioexec' \
        --exclude='/wine' \
        --exclude='/go-build' \
        --exclude='/rclone' \
        --exclude='/spotify' \
        --exclude='/.nv' \
        "$TMP_DIR/" "$PERSIST_DIR"
fi